An operation generally performed during the manufacture of a photographic camera 1 is the focusing of a taking lens 2 with respect to a film plane within the camera. A focus fixture set-up as shown in FIG. 1 generally includes a target 3 comprising light 4 and dark 5 bands, a light source 6 for illuminating the target 3 and a detector 7 at the film plane. The target 3 is rotated at a specific velocity and the detector 7 measures the contrast between the light 4 and dark 5 bands. This is generally known as measuring the Modulation Transfer Function (MTF) response of the lens. The taking lens 2 of the camera 1 will be moved along its optical axis until a predetermined contrast has been measured by the detector 7 at the film plane, thus the taking lens 2 will be correctly calibrated.
It can be seen from the description of the focus fixture above that a shutter mechanism of a camera should remain open for the duration of the calibration of the taking lens.